1. Field of the Invention
The present invention relates to a pulse width modulation (PWM) current controlling apparatus for controlling PWM currents flowing through a load.
2. Description of the Related Art
Current controlling apparatuses have been known to compare a load current flowing through a load with an aimed current, so that the load current is brought close to the aimed current (see: JP-5-137255A, JP-5-307702A and JP-5-328070A).
A first PWM current controlling apparatus is constructed by a reference digital-to-analog converter for performing a digital-to-analog conversion upon digital data to generate a reference level signal, a triangular-wave signal generating circuit for generating a triangular-wave signal in accordance with a PWM timing signal, a sensing circuit for sensing a load current flowing through a load such as a motor to generate a sense signal in accordance with the load current, an adder for adding the triangular-wave signal to the reference level signal, to thereby generate a reference signal, a comparator for comparing the sense signal with the reference signal, to thereby generate a PWM signal, a predriver for generating a plurality of PWM current controlling signals in accordance with the PWM signal, and a bridge circuit including semiconductor elements connected to the load. In this case, the semiconductor elements are driven by the PWM current controlling signals. This will be explained later in detail.
In the above-described first prior art PWM current controlling apparatus, however, it is impossible to make the load current coincide with an aimed current under any load condition over a wide load current range.
In order to make the load current coincide with an aimed currents in a second prior art PWM current controlling apparatus, the reference level signal is also directly supplied to the comparator as well as the reference signal, so that the reference signal is substantially corrected by the reference level signal. This also will be explained later in detail.